Phosphocalcic ceramics first appeared in the field of biomaterials around twenty years ago. They make it possible to offset the drawbacks of biologic grafts (autografts (also known as autogenous or autologous grafts), allografts (also known as allogenic or homologous grafts) and xenografts) while promoting bone reconstructing. Indeed autografts require a second surgical operation on the donor site; they only enable, in general, the filling of small volumes due to the little amount of tissue available, said tissue sometimes being of poor quality particularly in elderly patients, and they are associated with a certain morbidity rate. Allografting leads to an often reduced re-colonization [Enneking W. F., Journal of bone and joint surgery, 73-A, 8, 1123-1141, 1991] and infection risks that can be responsible for massive osteolyses encountered in some patients.
Consequently, synthetic ceramics are commonly used by surgeons (orthopedic, maxillofacial, plastic or dental), since a loss of bone substance requires filling.
Hydroxyapatite (HA) and tricalcic phosphate (TCP) are the two most widely used calcium phosphates in the field of biomaterials [Li Shihong, De Groot Klaas, Layrolle Pierre, Van Blitterswijk Clamens, De Wijn Joost; Porous ceramic body, U.S. Pat. No. 6,479,418, 2002], even though these two phases have very different physical-chemical properties.
Hydroxyapatite may be considered as one of the least soluble calcium phosphates and it is a non-bioresorbable biomaterial. Consequently, hydroxyapatite is commonly used for coating metal prostheses so as to enhance the biointegration of the material. TCP, which for its part is much more soluble, makes up a resorbable material that is progressively replaced by bone. However, its resorption rate cannot be modulated (“Bioceramics and their clinical applications”, Ed. T. Kokubo, CRC Press, 2008).
Biphasic ceramics made up of a variable mixture of HA and TCP enable the bioresorbability to be modulated as a function of the level of TCP used and for this reason they have enjoyed considerable success in the field of biomaterials (“Bioceramics and their clinical applications”, Ed. T. Kokubo, CRC Press, 2008).
All of these ceramics are obtained by sintering at high temperature and the biological activity of such type of material is limited on account of the low specific surface of the sintered materials and their weak interaction with the various proteins and growth factors responsible for adhesion, proliferation and cell expression. They are moreover quite far removed from bone mineral and behave differently, both in chemical and biological terms.
Most known nanocrystalline apatite deposition procedures make use of supersaturated calcium phosphate solutions that are difficult to use industrially, with processing times sometimes lasting several days. The most widely employed method consists in using SBF (Simulated Body Fluid) (Kokubo T, Takadama H (2006), How useful is SBF in predicting in vivo bone bioactivity, Biomaterials 27, 2907-2915). Other methods, on the same principle, have been developed using more concentrated solutions (Layrolle P, Stigter M, De Groot K, Liu Y, Method for applying a bioactive coating on a medical device, 2006, U.S. Pat. No. 6,994,883 and Layrolle P, de Groot K, de Bruijn J, van Blitterswijk C, Huipin Y, Method for coating medical implants, 2004, U.S. Pat. No. 6,733,503, continuation of 2001, U.S. Pat. No. 6,207,218; and also Li P, Wen H B, Hippensteel E, Biological agent-containing ceramic coating and method, 2006, U.S. Pat. No. 7,087,086, and Li P, Bioactive ceramic coating and method, 2003, U.S. Pat. No. 6,569,589). These methods have moreover been rarely used to coat the inside of ceramic pores.
Simple and rapid methods enabling a biological activation of the surface of sintered porous ceramics thus do not exist. The aforementioned patents have not as yet been applied industrially. Moreover, the apatites obtained by these methods are generally mature and have a lower reactivity than those precipitated and deposited by the present method, which offers the possibility of choosing the maturation time.